In the production of microelectronic devices, one or more metals and/or alloys may be deposited on a substrate for a variety of purposes. Typically, it is desirable for metal to be deposited only in certain locations and not in others. Metal deposited outside of desired locations may not only lead to defects in semiconductor devices, but may also cause contamination of apparatus utilized during and/or after plating. Additionally, material deposited on areas where it is not meant to be deposited may not adhere properly. For example, copper has poor adhesion to most insulators.
As a result, copper deposited at the edge or backside or other areas of a wafer or substrate may flake off of the substrate, contaminating the deposition equipment and/or other subsequent apparatus and equipment that are exposed to the wafer or substrate. Particulate contamination of devices may result in degraded chip yield loss, performance, and expensive equipment clean-up operations. Also, expensive operating protocols may then be established to minimize or reduce particulate problems.
Operations that have been utilized to remove metal deposited at desired locations include specialized backside spray tools and/or edge grinding at edge stations. A common method to help prevent unwanted metal deposition at edges of wafers includes the use of a clamp ring or shadow ring utilized during metal sputtering or CVD deposition. FIGS. 1a, 1b, 1c, and 1d illustrate an example of such a device. However, such mechanical contraptions are expensive. Other cleaning methods utilize an inert gas curtain to prevent metal deposition near the edge, rim, or backside of wafers.
Additionally, utilizing a clamp ring or shadow ring still generates particulates, because metal deposition on such rings flakes off as well. Furthermore, clamp rings and shadow rings need to be maintained.
Clamp and shadow rings operate by excluding a portion of the wafer edge. For example, a clamp or shadow ring could exclude about 2 to about 5 mm of a wafer edge. Such exclusion reduces the surface area available for forming chips. As a result, the number of chips produced from a wafer may be reduced when utilizing a clamp ring or shadow ring. A clamp ring or shadow ring may also affect the uniformity and the profile of the deposit.
Also, straggling metal is occasionally deposited on the surface of wafers, at regions under the clamp ring. These spurious deposits may stick poorly to the underside of the clamp ring. As these deposits accumulate, the clamp ring may become an additional source of defects and/or a particle generator, contaminating different wafers. When the clamp ring underside deposit becomes sufficiently thick, the clamp ring may lose its effectiveness.
An additional problem related to unwanted metal deposition is tool cross-contamination and line contamination. These problems may be caused by improperly deposited metal on a substrate randomly falling off to surfaces where they are least desired to be. An example of such an undesirable surface includes a surface on a robot handler.